Multiconfiguration ionization source

ABSTRACT

This is an ion-producing source having a distinct chemical ionization configuration and a distinct electron impact configuration. In this source, a hollow chamber including an ion source and a source of sample molecules receives a hollow, slidable cylindrical member having a chemical ionization chamber within it. Orifices in the chamber and the cylindrical member connect the chemical ionization source chamber to the electron source and to the sample molecule source when the cylindrical member is pulled to one position. When the cylindrical member is pulled to another position, the slidable cylindrical member and the inside walls of the chamber define the ionization region to which the electron source and the sample molecule source are directly connected. By moving the cylindrical member, the ionization source can be changed from a chemical ionization source to an electron impact source.

United States Patent Kruger et al.

May 27, 1975 MULTICONFIGURATION IONIZATION Primary ExaminerJames W.Lawrence SOURCE Assistant Examiner-B. C. Anderson [75] Inventors:William P. Kruger, Los Altos Hills; Attorney Agent or Flrmpamck BarrenJohn A. Michnowicz, Santa Clara, both of Calif. ABSTRACT [73] Assignee:newletbpackard Company, Palo This is an ion-producing source having adistinct Alto Calm chemical ionization configuration and a distinctelectron impact configuration. In this source, a hollow i 1 Flledi g- 91973 chamber including an ion source and a source of sam- [21] APPL No:391,721 ple molecules receives a hollow, slidable cylindrical memberhaving a chemical ionization chamber within it. Orifices in the chamberand the cylindrical member I Cl 250/423; 250/427 connect the chemicalionization source chamber to [51 1 Int. Cl. the electron sgurce and tothe sample molecule ource Field of Search 250/424, 423, 427 when thecylindrical member is pulled to one position.

When the cylindrical member is pulled to another pol Referemes Ciedsition, the slidable cylindrical member and the inside UNITED STATESPATENTS walls of the chamber define the ionization region to 3.11559112/1963 Brunnee a. 250/423 WhiCh the electron mum and the Samplemolecule 3355.587 11/1967 j k n 25 7 source are directly connected. Bymoving the cylindri- 3.405.263 /1968 Wanless etalm. 250/285 cal member.the ionization source can be changed 3.553. 1/197! Tieman 250/427 from achemical ionization source to an electron im- MLlIlSOI'l pact ource3.582.645 6/197l Brunnee et al. n i 250/423 10 Claims, 2 Drawing Figures5 46 l2 I6 44 ii t I I I I 48 55 flfi 4 34 Emma/232 I H% I/lII/I/I/III/If J I 73 S 38 24 {t ngo 72 O 36 [17/ l\\\\\\\ PATH-1TH m 2 7 msigure 1 igure 2 1 MULTICONFIGURATION IONIZATION SOURCE BACKGROUND OF THEINVENTION Ion sources are employed with mass spectrometers in theanalysis of substances. Commonly used sources are the electron impactsource and the chemical ionization source. The first one has a largeelectron entrance, :1 large ion exit. and an ionization region where theincoming electrons fragment as well as ionize vapor molecules thusproviding a large quantity of information which does not necessarilygive clear indication of the identity of a substance. The chemicalionization source has, on the other hand, a small electron entrance, asmall ion exit, and an ionization region where the pres sure can bemaintained at such levels that ionmolecule collisions are extremelylikely to occur, such collisions leading to ready identification of themolecular weight of a substance.

Operation of a mass spectrometer alternately with electron impact andchemical ionization sources has required many hours of down time duringwhich the operation of the spectrometer stops. An object of thisinvention is to permit changing between the electron impact and thechemical ionization configurations with minimal interruption ofoperation of the mass spectrometer.

BRIEF SUMMARY OF THE INVENTION According to the preferred embodiment,this inven tion provides an ionization source with two distinct ionization chambers, one which operates as an electron impact ionizationsource and the other as a chemical ionization source. The invention maybe used with a mass spectrometer and changes in configuration can bemade easily and quickly. The main elements of the invention include ahollow chamber having a plurality of orifices transverse to thelongitudinal axis of the chamber. One of the orifices contains anelectron source, and another one is a gaseous sample inlet. A hollowslidable cylindrical member having smaller transverse orifices thanthose in the hollow chamber fits inside the hollow chamber. At one ofits ends, the cylindrical member has two electrode inserts separatedfrom each other along the longitudinal axis and defining a firstionization region between them and the inside walls of the hollowcylindrical member, This region is connected to the sample inlet orificeand to the electron source orifice when the hollow cylinder is in afirst position. A second ionization region is defined by the insidewalls of the hollow chamber, the outer electrode insert of thecylindrical member, and the open end of the hollow chamber, when thecylindrical member is in a second position. This second region isdirectly connected to the electron source orifice and to the sampleinlet. In this manner, when the cylindrical member is in the firstposition. the source operates as a chemical ionization source and whenthe cylindrical member is in the second position, the source operates asan electron impact source. The position of the cylindrical member can bechanged quickly and easily by simply pushing or pulling a handleattached to the cylinder.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross-sectional view of thepreferred embodiment of the present invention in the chemical ionizationconfiguration.

FIG. 2 shows the apparatus of FIG. I in the electron impactconfiguration.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. I and 2 show a vacuumenvelope I4 which is connected to an ordinary vacuum pump through a port9 for evacuating air from the envelope. An ion chamber I6, which may bea stainless steel tube. is supported within envelope I4 by a supportmember I2 and has orifices, l7, I7 and 23 transverse to its longitudinalaxis. Orifice [7 contains a filament 18 near the periphery of ionchamber 16 and near an end 19 of ion chamber I6. Orifice 23 is an inletfor samples to be ionized. The ion chamber 16 has a preferablycylindrical bore 24 along the longitudinal axis. Filament orifice I7intersects bore 24 near end 19.

A hollow member 28 fits slidably inside bore 24, which member may bemade of stainless steel tubingv Electrode inserts 35 and 36 aresupported by and fastened to the inside of slide member 28 by insulatorspreferably made of ceramic. Insert 35 is located at end 21 of member 28and has a passage 34 through it. Insert 36 is spaced apart fom insert 35and has a passage 39 through it. A connector 38 passes through passage39 and engages passage 34 in insert 35 when member 28 has been moved tothe left as shown in FIG. 2. A spring 40 attaches connector 38 to a baseblock 42, and this block is in turn affixed to but electricallyinsulated from chamber 16. Slide member 28 has a slot 44 through whichbase block 42 passes. The external surface of hollow member 28 ispreferably hardened to prevent galling or binding with chamber 16. Ahandle 48 attaches to end 53 of hollow member 28 and is used to displacethis member from the first position to the second position as shown inFIGS. 1 and 2 respectively. A bellows 46 surrounds handle 48 andconnects the end 53 of hollow member 28 with a wall 55 of vacuumenvelope 14. A support member 12 surrounds the bellows 46 and affixesthe chamber 16 to wall 55. A pivot axle between a support member 71 andan arm 72 permits pulling or pushing arm 72, which is connected tohandle 48, for placing cylinder 28 in either the chemical ionizationconfiguration as shown in FIG. I or the electron impact configuration asshown in FIG. 2. Arm 72 is connected to handle 48 by a Vernier screwarrangement 73 for making fine alignment adjustments of electron passage32 with filament orifice 17.

As shown in FIG, I, electrode inserts 35 and 36 and the inner peripheryof hollow member 28 define a first ionization region 30 when hollowmember 28 is to the right, as in FIG. 1. A second ionization region 30'is defined by the interior walls of chamber body 16, the electrodeinsert 35 to the left, and the open end I9 of chamber 16 to the right. Apassage 32 through the wall of hollow member 28 permits entry ofelectrons into the ionization region 30 from orifice 17 when hollowmember 28 is to the rightv A sample inlet 23 through the walls of ionchamber 16 permits entry of an ionization sample into ionization region30 when cylinder 28 is to the left as shown in FIG. 2. Sample inlet 23,and sample inlet 20 passing through the walls of hollow member 28,permit entry of an ionization sample into ionization region 30, whenhollow member 28 is to the right as shown in FIG. 1. A passage 34permits exit of ions from the ionization region 30 to an ion lensassembly 26. Both passages 32 and 34 may have a conical configuration toimprove entry of the electrons through the first passage and exit oftheions through the second passage. Passages 32 and 34, the electronentrance and ion exit passages respectively of the chemical ioniza tionchamber. are much smaller than the respective passages 17 and 2] of theelectron impact chamber. The smaller size of passages 32 and 34 permitsmaintaining a higher pressure in ionization region 30 than in ionizationregion 30'.

Magnets 52 and 52' are located adjacent to filament l8 and to anelectron collector 50, respectively. which is disposed on the peripheryof chamber [6 diametrically opposed to filament 18. The magnets directan electron beam from the filament to the collector. The ion lensassembly 26, adjacent to end 19, extends away from chamber 16 and. whenthe appropriate potentials are applied, focuses ions emerging fromionization re gions 30 and 30 into a mass filter for analysis (notshown).

A potential source 70 is connected to insert 35 by connector 38 tomaintain insert 35 at a potential for re pelling ions when the hollowmember 28 is to the left. as shown in FlG. 2. When the hollow member 28is to the right. connector 38 engages only insert 36 to maintain arepelling potential on this insert. which insert b now becomes arepeller electrode.

When the hollow cylindrical member is to the left the ionization sourceis operating in the electron im pact configuration where the pressureinside ionization region 30' is about l Torr; the ionization electronshave energies of about 70 eV; and mean-free-paths of about 2 X l0inches. The electrons in this configuration fragment the samplemolecules and produce many ions whose mass'to-charge ratios do notnecessarily correspond to the molecular weight of the sample. When thehollow cylindrical member is to the right, the ionization source isoperating in the chemical ioniza tion configuration where the pressurein ionization re gion 30 is up to 1.0 Torr; the ionization electronshave energies of about 100 to 500 eV; and short mean-freepaths of about2 X inches. The electrons in this configuration do not fragment thesample molecules as much as in the electron impact configuration. butproduce an abundance of ions whose mass-tocharge ratio corresponds moreaccurately to the molecular weight of the sample.

We claim:

I. A multiconfiguration. multimode ionization source comprising:

a vacuum tight envelope;

a chamber having walls surrounding an internal cavity and mounted withinthe envelope. said chamber having a plurality of openings;

an electron source disposed exterior to the chamber for supplyingelectrons to the chamber through a first of said openings;

sample inlet means for supplying a gaseous sample through a second ofsaid openings for reaction with the electrons inside the chamber tocreate ions. said ions exiting through a third of said openings;

aperture control means for changing the size of the first and thirdopenings for changing the pressure ofthe sample in the chamber. therebychanging the operating mode of the source from a first to a sec ondionization mode; and

ion repelling means disposed inside the chamber for repeliing ions outof the chamber through the third opening.

2. A muiticonfiguration ionization source as in claim I wherein:

the aperture control means comprises a movable member within thechamber. said member having an electron opening smaller than said firstopening and also having an ion opening smaller than said third opening:

said electrons from the source pass through the electron opening and thefirst opening when said movable member is in a first position;

said ions in the cavity pass through the ion opening and the thirdopening when the movable member is in the first position; and

said electrons pass through only the first opening and said ions passthrough only the third opening when the movable member is in a secondposition.

3. A multiconfiguration ionization source as in claim 2 wherein themovable member comprises a hollow slidable cylinder having an ion exitend and a handie end.

4. A multiconfiguration ionization source as in claim 3 including:

a bellows having a first end attached to the handle end of the cylinderand by a second end to a wall of the vacuum tight envelope; and

a handle surrounded by the bellows, one end of said handle attaches tothe cylinder while the other end of the the handle protrudes throughsaid vacuum tight envelope wall.

5. A multiconfiguration ionization source as in claim 4 wherein there isan electron collector opposite the electron source. and wherein thereare magnets disposed adjacent the electron source and the electroncollector to direct the electrons from the electron source.

6. A multiconfiguration ionization source as in claim 5 wherein an ionlens assembly is attached to the electron source end of the chamber forfocusing ions into a utilization device.

7. A multiconfiguration ionization source as in claim 6 wherein avernier adjustment screw is attached to said handle for making fineadjustments in the position of the cylinder for aligning the electronopening with the electron source.

8. A multiconfiguration ionization source as in claim 3 wherein the ionrepelling means comprises:

a first and second repeller electrode mounted in and electricallyinsulated from the hollow slidable cylinder'. and

a connector connectable to a source of potential for making anelectrical connection with the first repeller electrode when theslidable cylinder is in the first position and with the second repellerelectrode when the slidable cylinder is in the second position.

9. A multiconfiguration ionization source as in claim 8 wherein said ionopening is in the second repeller electrode.

[0. A multiconfiguration ionization source as in claim 1 wherein thefirst ionization mode is a chemical ionization mode and the secondionization mode is an electron impact ionization mode.

t t t

1. A multiconfiguration, multimode ionization source comprising: a vacuum tight envelope; a chamber having walls surrounding an internal cavity and mounted within the envelope, said chamber having a plurality of openings; an electron source disposed exterior to the chamber for supplying electrons to the chamber through a first of said openings; sample inlet means for supplying a gaseous sample through a second of said openings for reaction with the electrons inside the chamber to create ions, said ions exiting through a third of said openings; aperture control means for changing the size of the first and third openings for changing the pressure of the sample in the chamber, thereby changing the operating mode of the source from a first to a second ionization mode; and ion repelling means disposed inside the chamber for repelling ions out of the chamber through the third opening.
 2. A multiconfiguration ionization source as in claim 1 wherein: the aperture control means comprises a movable member within the chamber, said member having an electron opening smaller than said first opening and also having an ion opening smaller than said third opening; said electrons from the source pass through the electron opening and the first opening when said movable member is in a first position; said ions in the cavity pass through the ion oPening and the third opening when the movable member is in the first position; and said electrons pass through only the first opening and said ions pass through only the third opening when the movable member is in a second position.
 3. A multiconfiguration ionization source as in claim 2 wherein the movable member comprises a hollow slidable cylinder having an ion exit end and a handle end.
 4. A multiconfiguration ionization source as in claim 3 including: a bellows having a first end attached to the handle end of the cylinder and by a second end to a wall of the vacuum tight envelope; and a handle surrounded by the bellows, one end of said handle attaches to the cylinder while the other end of the the handle protrudes through said vacuum tight envelope wall.
 5. A multiconfiguration ionization source as in claim 4 wherein there is an electron collector opposite the electron source, and wherein there are magnets disposed adjacent the electron source and the electron collector to direct the electrons from the electron source.
 6. A multiconfiguration ionization source as in claim 5 wherein an ion lens assembly is attached to the electron source end of the chamber for focusing ions into a utilization device.
 7. A multiconfiguration ionization source as in claim 6 wherein a vernier adjustment screw is attached to said handle for making fine adjustments in the position of the cylinder for aligning the electron opening with the electron source.
 8. A multiconfiguration ionization source as in claim 3 wherein the ion repelling means comprises: a first and second repeller electrode mounted in and electrically insulated from the hollow slidable cylinder; and a connector connectable to a source of potential for making an electrical connection with the first repeller electrode when the slidable cylinder is in the first position and with the second repeller electrode when the slidable cylinder is in the second position.
 9. A multiconfiguration ionization source as in claim 8 wherein said ion opening is in the second repeller electrode.
 10. A multiconfiguration ionization source as in claim 1 wherein the first ionization mode is a chemical ionization mode and the second ionization mode is an electron impact ionization mode. 